To improve engine control functions, an electronic control unit (ECU) with a microcomputer has been used in recent years for executing control programs, such as control of ignition timing in an engine, control of valve opening and closing timing, and/or control of fuel injection in an electronic fuel injector (EFI) for an automobile (hereinafter, referred to as a "vehicle"). The ECU is connected to sensors, such as a temperature sensor for detecting a temperature of engine cooling water, an engine-speed sensor for detecting an engine speed, a vehicle-speed sensor for detecting a vehicle speed, and an O2 sensor for detecting an oxygen concentration in exhaust gas. The ECU is also connected to switches such as a brake switch for detecting that a driver has stepped on a brake pedal. The ECU thus executes various kinds of controls based on detection signals output from the sensors and others.
On the production line where vehicles with such an ECU are manufactured, in the final test process after assembled, it should be diagnosed whether or not each of sensor and the like, and the ECU itself functions normally. For example, Japanese patent publication No. Hei 3-59372 proposes a diagnostic method in which a diagnostic apparatus with a microcomputer executes a vehicle diagnostic program to diagnose a desired diagnostic item at scheduled timing.
In a failure diagnosis related to a plurality of diagnostic items, for example, as disclosed in Japanese patent publication No. Sho 61-25091, the plurality of diagnostic items are diagnosed in predetermined order and the results of pass/failure or displayed judgment in respective diagnostic items are output one by one.
A typical checking (diagnostic) apparatus with a microcomputer is generally designed to make its display part show a menu screen when the operator turns on a power switch of the checking apparatus after connected to a machinery to be checked. On the menu screen, a list of many available functions is displayed, such as "Self-Diagnostic Function", "Memory Check Function" and "Mode Select Function", including a desired checking function. Then the operator selects a desired checking function through a key operation to start a test program for executing the selected checking function.
Some of such vehicle diagnostic items require particular preconditions. For example, an "Ne Diagnosis" to determine whether or not an engine speed Ne at idling time is in a given range or not must be executed under the condition that the engine has been warmed up adequately. Some other diagnostic items require no precondition and are allowed to complete the diagnosis for an instant, such as a "Brake Switch Diagnosis" to diagnose an opening and closing function of a brake switch. It should be noted that the "Ne Diagnosis" is automatically executed according to the program, and the operator has nothing to do during execution of this program but keep the engine idling.
When a vehicle diagnostic program is started, the result of the "Switch Diagnosis" can be obtained in a very short time after starting the diagnosis, but the "Ne Diagnosis" cannot be even started until the preconditions, such as to warm up the engine adequately, are satisfied. Therefore, even if the "Ne diagnosis" is not judged to be passed, it will require much operator's labor to determine whether the judgment is caused by a fault of the idling speed Ne or the diagnosis itself that has not been executed yet because the engine has not been warmed up adequately.
When such a plurality of diagnostic items are required, the sequence of items to be diagnosed is predetermined in a conventional vehicle diagnostic program. It is therefore impossible to diagnose a subsequent item before the previous item is diagnosed as being passed or failed. If the "Brake Switch Diagnosis" is prearranged to be executed after the "Ne Diagnosis", the operator can not start executing the "Brake Switch Diagnosis" until the "Ne Diagnosis" has been completed after warming up the engine, and is kept waiting wastefully during the execution of the "Ne Diagnosis". This causes long compulsory working-hours of the operator.
When the sequence of items to be diagnosed is predetermined, as discussed above, the operator is restricted by the sequence and timing of operations to be performed for each diagnostic item. This also raises a problem that the work efficiency is reduced.
The combination of the vehicle diagnostic items to be executed depends on the specification of each individual vehicle, including the type of the vehicle construction such as the transmission type of manual or automatic, and its designation. Such conditions of each individual vehicle have been registered as model information in the ECU of the vehicle. In conventional vehicle diagnostic methods, the type of vehicle construction and designation are recognized and items to be diagnosed are selected based on the model information so that only the diagnoses related to the selected items is executed. If there is comparison data to be used only in a specific model for quality judgment, the operator must check the comparison data with corresponding model information for each individual vehicle by referring to a manual, and this causes a complicated procedure.
The sequence of diagnoses to be executed in the final test process after assembled requires the diagnostic apparatus to be turned on for quite a long time, and when an internal battery is used to provide power for the diagnostic apparatus, the operator must change the battery frequently. It is therefore desirable to feed power from a battery on the vehicle side to the diagnostic apparatus through a communication cable.
In this case, since the vehicle is a commodity, if power feeding to the diagnostic apparatus is dependent on the battery on the vehicle side, it may be good practice to turn off the power switch of the diagnostic apparatus when the operator takes a rest or has a lunch so that the power dissipation is made as low as possible. But actually the diagnostic apparatus must be kept on during a recess since the diagnostic results obtained before then are lost each time the power switch of the diagnostic apparatus is turned off. Further, when the operator stops the diagnostic process for taking a rest, an unchanged screen remains on the display during the recess, so that the display screen may be burned out.
To solve such problems, there has been proposed an additional function by which the diagnostic process goes to a standby mode to turn off the display screen, for example, when no key operation is done for a given time, on purpose to reduce the power dissipation and protect the display screen. In conventional diagnostic apparatuses, however, the operator must operate a key or keys for returning from the standby mode to the diagnostic mode, and this makes the procedure complicated.
Still another problem arises, when the power feeding to the diagnostic apparatus is dependent on the battery on the vehicle side, that the power-on operation must be done each time the diagnostic apparatus is changed for another vehicle to be diagnosed. Further, since the conventional checking (diagnostic) apparatuses are designed to display a first menu screen at all times after power-on, the menu selection must be made each time the diagnostic apparatus is changed, and this makes the operation complicated. It is possible to change the program such that the diagnostic process is started at the same time when the diagnostic apparatus is turned on, but this sacrifices capability in selecting other functions than diagnoses.